This invention relates to a process for producing a pyrido[1,2-a]pyrimidine derivative which is useful as an antiallergic agent.
Pyrido[1,2-a]pyrimidine derivatives and salts thereof are known as drugs having antiallergic activity. Various antiallergic agents containing such compounds as an effective component are widely used. Processes for producing such compounds are disclosed, for example, in Japanese Patent Unexamined Publication Nos. 63-183581, 63-246374, 63-246375, etc. According to these processes, pyrimidine derivatives or pyridine derivatives containing a cyano group are synthesized from commercially available compounds, followed by reaction with hydrazoic acid or a salt thereof to form a tetrazole ring, thus giving the desired compounds by multistep synthesis. Further, U.S. Pat, No. 4,474,953 discloses a process for producing a pyrido[1,2-a]pyrimidine derivative by reacting a 2-aminopyridine derivative, a tetrazol-5-yl acetic acid ester and an orthoformic acid ester in the presence of a Lewis acid to yield a 3-[N-(2-pyridyl)-amino]-2-(1 H-tetrazol-5-yl)acrylate derivative, which is then separated and heated at 100.degree. to 150.degree. C. in polyphosphoric acid for ring closure. This process employs a two-step reaction using different catalysts in both steps with complicated procedures.
Since pyrido[1,2-alpyrimidine derivatives have a very complicated structure, these compounds have been usually synthesized by multi-step reactions, resulting in increasing in production time, man power, production apparatus, and production cost.